The invention relates to a method for determining a rotor temperature of an electric machine, in particular an asynchronous machine, wherein the rotor temperature is determined at least as a function of reactive powers and/or as a function of losses of the electric machine.
The invention further relates to a corresponding device and to a computer program and a computer program product.
The rotor temperature of an asynchronous machine provides an important piece of information both with regard to the torque accuracy in the case of a field-oriented control and with regard to the thermal protection of the electric machine. For reasons of cost, a telemetry system is not used, as a rule, in mass production for measuring the rotor temperature. Therefore, the rotor temperature is usually determined by means of model calculations. It is known that the rotor temperature is ascertained by means of an electromagnetic model, which determines the rotor temperature as a function of reactive powers of the electric machine, or as a function of a thermal model which determines the rotor temperature as a function of losses. The electromagnetic model is based on the reconciliation between a reactive power calculated on the basis of phase voltage and current and a reactive power calculated on the basis of a flux model which is dependent on motor parameters, stator frequency, and current. A combination of these methods, which is intended to expand their functional range, is also already known.
The thermal model requires losses as input values, wherein the accuracy of the loss calculation has a substantial influence on the estimated or determined rotor temperature. An exact analytical calculation or the experimental ascertainment of losses in the electric machine, in particular in the asynchronous machine, is very time-consuming, however.